Losing Sense of Smell, Taste, May Be Early Signs of COVID-19

(Reuters Health) - Loss of the senses of smell and taste may be an early sign of infection with SARS-CoV-2, the virus that causes COVID-19, Italian researchers report in Clinical Infectious Diseases.

In a letter, Dr. Andrea Giacomelli, a research fellow at the Dipartimento di Scienze Biomediche e Cliniche L. Sacco at the University of Milan, and colleagues write that identifying minor signs and symptoms of COVID-19 may be useful as a screening tool, particularly for patients in earlier stages of infection.

Of 59 hospitalized COVID-19 patients surveyed, Dr. Giacomelli's team found that more than a third had issues with taste or smell either before or after being admitted.

"In a pandemic context, further investigations on non-hospitalized infected patients are required to ascertain if these symptoms, albeit unspecific, may represent a clinical screening tool to orientate testing of pauci-symptomatic individuals," Dr. Giacomelli said in an email. "We believe that the full characterization of the clinical course of the SARS-CoV-2 infection with regard to mild symptoms is of paramount importance to identify patients and pursue the optimal contact tracing."

On March 19, Giacomelli and colleagues questioned all COVID-19 patients at their institution able to give informed consent about their taste and smell symptoms. Patients were asked which, if any, olfactory and taste disorders they had experienced and the timing of those symptoms.

Among the surveyed patients, 20 (33.9%) reported at least one taste or olfactory disorder and 11 (18.6%) reported experiencing both. Twelve patients (20.3%) said they experienced the symptoms prior to being admitted to the hospital and the other eight reported that symptoms started after they were admitted.

Alterations to the sense of taste occurred more frequently (91%) before hospitalization. After hospitalization, taste and olfactory alteration appeared with equal frequency.

Females reported changes in the senses of smell and taste at twice the rate of males: 10 out of 19 women (52.6%) and 10 out of 40 men (25%) among the 59 participants reported alterations. Patients with at least one taste or olfactory disorder also tended to be younger (median age 56 years) than those who didn't experience these symptoms (median age 66 years).

Olfactory and taste disorders related to viral infections are well known, and a mouse model has shown that the nerves in the olfactory bulb can be penetrated by the original SARS-CoV-1 virus, the researchers note. "Moreover, angiotensin converting enzyme 2 receptor, which is used by SARS-CoV-2 to bind and penetrate into the cell, is widely expressed in the epithelial cells of the mucosal of oral cavity. These evidences could explain the underlying pathogenetic mechanism of taste and olfactory disorders in SARS-CoV-2 infection."

The authors should be commended for getting the report out so quickly, especially with everything they're dealing with in Italy, said Dr. Sara Keller an assistant professor of infectious disease at Johns Hopkins School of Medicine, in Baltimore.

One issue, Dr. Keller said, is that the questionnaire was given only to people who were hospitalized, so we don't know if people have this symptom even if they are not severely ill.

"As the weeks go on it will be very interesting and important to address this," she said. "There's been a lot of discussion in physician communities whether problems with smelling and tasting are common in those with relatively minor disease. That's an important question that needs to be worked out."

Another important question, Dr. Keller said, is whether people experiencing issues with smell and taste have runny noses. "There are some anecdotal reports that suggest this is something that happens in the absence of a runny nose and maybe the virus is impacting the nerves involved in smell and taste."

Physicians have been discussing this topic on social media sites, said Dr. Eric Wang, an associate professor of otolaryngology at the University of Pittsburgh and vice chair of the UPMC department of otolaryngology's clinical operations.

"It's known in general that viruses are one of the more common causes of losing the sense of smell," Dr. Wang said. "The nerve involved in the sense of smell is unusual. It's the only one that comes out to the surface. At its end are fingers that go down the boney canal and come to the surface of the mucosal lining. Small molecules interact with the nerve which turns that interaction into electrical signals that our brain interprets as smell."

Some preliminary non-peer-reviewed publications have suggested that interactions between COVID-19 and the olfactory bulb lead to a loss of smell, Dr. Wang said.

Because of all that suggestive data, when people call in complaining of a loss of the sense of smell, Dr. Wang and others are recommending self-quarantine if the symptom is new.

"So, it's not like we're getting 100 calls a day, but we are getting a few," he said. "So, we say, if you want to do something for your neighbors and other people around you, you should consider staying in for the two weeks."